Fake Law Log Pot

DolbyR · 17th January 2006, 09:33 AM

ive heard of some resistors tweaks to make from a Lin a pot, a Log one. Is it possible also to make a fake reverse Log pot from a linear one? And how would this happen?

richie00boy · 17th January 2006, 09:57 AM

Just connect resistor wiper to input instead of wiper to ground

DolbyR · 17th January 2006, 09:59 AM

so no additional resistor is needed to the pot? or a resistor from wiper to input?

I_Forgot · 17th January 2006, 12:49 PM

See here:
http://www.geofex.com/Article_Folder...s/potscret.htm

Like the other guy says, politics aside, google is a wonderful thing...

If you have a spreadsheet program you can easily calculate and plot the curve that you will get- it's all Ohms law...

I_F

sam9 · 17th January 2006, 12:55 PM

Go to http://sound.westhost.com and look up Project 01. Not only can you make a linear pot behave like a log pot, it is argued that the results are moe accurate than a real log pot. This may be especially true with a double-ganged pot.

BTW, I only buy linear pots any more. It's not really all that big a deal in normal use but I definately discern that the "fake" log-pots respond more evenly than "real" ones.

richie00boy · 17th January 2006, 02:06 PM

He knows about law faking lin to get a log pot

His question was how do you make an antilog pot.

Bobken · 17th January 2006, 02:34 PM

Hi,

Please note that any 'reverse log' pot made in this way (law-faking) will only work as a full 3 terminal voltage-divider arrangement.

It doesn't work properly as a simple two terminal 'variable resistor' arrangement as the change in resistance which is more pronounced per unit of rotation at one extreme, will be at the 'wrong end' of rotation, unfortunately.

I know because I tried it out quite recently, myself, much to my disappointment, and when I subsequently made some suitable calculations of the parallel resistances involved at different points of rotation, it was quite clear to me why this is the case.

Also, it cannot simply be corrected by reversing the connections for a two terminal arrangement, either, as this makes no difference, of course.

00940 · 17th January 2006, 10:55 PM

http://tangentsoft.net/audio/atten.html worth reading.

17th January 2006, 09:33 AM	#1
DolbyR diyAudio Member Join Date: Oct 2005	Fake Law Log Pot ive heard of some resistors tweaks to make from a Lin a pot, a Log one. Is it possible also to make a fake reverse Log pot from a linear one? And how would this happen?

17th January 2006, 09:57 AM	#2
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Just connect resistor wiper to input instead of wiper to ground __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

17th January 2006, 02:06 PM	#6
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	He knows about law faking lin to get a log pot His question was how do you make an antilog pot. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

17th January 2006, 02:34 PM	#7
Bobken diyAudio Member Join Date: Dec 2002 Location: UK	Hi, Please note that any 'reverse log' pot made in this way (law-faking) will only work as a full 3 terminal voltage-divider arrangement. It doesn't work properly as a simple two terminal 'variable resistor' arrangement as the change in resistance which is more pronounced per unit of rotation at one extreme, will be at the 'wrong end' of rotation, unfortunately. I know because I tried it out quite recently, myself, much to my disappointment, and when I subsequently made some suitable calculations of the parallel resistances involved at different points of rotation, it was quite clear to me why this is the case. Also, it cannot simply be corrected by reversing the connections for a two terminal arrangement, either, as this makes no difference, of course. __________________ Bob

17th January 2006, 10:55 PM	#8
00940 diyAudio Member Join Date: Sep 2003 Location: Paris	http://tangentsoft.net/audio/atten.html worth reading. __________________ Ben.


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

17th January 2006, 09:59 AM	#3
DolbyR diyAudio Member Join Date: Oct 2005	so no additional resistor is needed to the pot? or a resistor from wiper to input?

17th January 2006, 12:49 PM	#4
I_Forgot diyAudio Member Join Date: Jan 2005 Location: Phoenix, Az.	See here: http://www.geofex.com/Article_Folder...s/potscret.htm Like the other guy says, politics aside, google is a wonderful thing... If you have a spreadsheet program you can easily calculate and plot the curve that you will get- it's all Ohms law... I_F

17th January 2006, 12:55 PM	#5
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	Go to http://sound.westhost.com and look up Project 01. Not only can you make a linear pot behave like a log pot, it is argued that the results are moe accurate than a real log pot. This may be especially true with a double-ganged pot. BTW, I only buy linear pots any more. It's not really all that big a deal in normal use but I definately discern that the "fake" log-pots respond more evenly than "real" ones.

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